Attempts will be undertaken to further purify the solubilized FSH receptor from calf testis. This will be done by application of standard techniques of protein chemistry with particular emphasis on affinity chromatography. Efforts will be directed toward reconstitution of a FSH-responsive solubilized receptor adenylate cyclase system. If successful, this should allow a detailed study of factors relating hormone binding and initiating of the primary post binding event in the sequalae of hormone action, activation of the adenylate cyclase. We will also pursue studies on tissue and serum factors which have been shown capable of inhibiting binding of FSH to testicular receptors in vitro. Our goal will be to characterize the putative inhibitory substance with regard to chemical nature (peptide, carbohydrate, etc.) and then to obtain evidence that the in vitro effects mentioned above can be duplicated in vivo, possibly resulting in an inhibition of spermatogenesis.